A watch dial is, for the most part, exactly what it appears to be: hands that glide or tick, stationary hour markers. On the Grönefeld 1941, one element is not. Near the nine o’clock position, a small three-armed device remains largely motionless — then, once every eight seconds, it spins rapidly and hums for an instant, a fleeting movement that appears and vanishes. The Grönefelds designed it to be seen: almost everyone else who has tackled the same problem has concealed the mechanism; they, on the other hand, have placed it on the dial. It is the regulator of a ‘remontoir d’égalité’, a constant-force mechanism near the balance wheel that governs the final stage of the energy released by the mainspring. Each hum marks the moment when the mainspring, via the gear train, recharges a small spring; for the eight seconds that follow, it is this spring – and no longer the barrel – that causes the balance wheel to oscillate. This monitoring process is made visible on the dial, so the owner can see that something upstream is being kept under control. To understand why something so small has occupied watchmakers for so long, one must follow that energy along its entire path.
Downstream of the mainspring barrel
What it protects against originates at the source, the moment a spring is wound. Inside the barrel, a steel strip is wound ever tighter upon itself until it stores a charge of potential energy, with only one possible direction: outwards, released as the spring uncoils and the barrel rotates. For much of the history of watchmaking, this was precisely where precision went to die. A watch that gains or loses a few seconds a day is, on land, a nuisance; at sea, it was a catastrophe. Longitude could only be determined by taking the time from a known location on board and comparing it, at midday, with the position of the local sun; and since the Earth rotates by fifteen degrees per hour, a four-minute error would cause a navigator to stray by a full degree — at the equator, sixty nautical miles between where he thought he was and where he actually was. Such an instrument had to maintain the time of a distant port with an accuracy of a few seconds for weeks at sea. Everything downstream of the barrel worked against it.
From the barrel, power is transmitted from wheel to wheel along a chain of pinions to the escapement, where it is consumed in the ticking that causes the balance wheel to oscillate — a long journey for something that is so easily lost. Every pin is subject to friction; every pair of meshing teeth returns slightly less than it received; the force arrives weakened by the journey. Worse still, it does not arrive uniformly: a newly wound mainspring pushes too hard, one that is nearly spent pushes barely at all, and only one that is half-wound behaves correctly. This irregularity is not merely an aesthetic flaw. If too much force is applied to the balance wheel, it swings through a wider arc; if the force is too weak, the arc narrows; and a balance wheel whose arc varies from hour to hour does not return to its starting point at exactly the same time — in short, the watch keeps changing its mind about how long a second lasts.
Correcting the source
The earliest solutions were based on a single premise: if the source is irregular, it must be corrected. The chain and fusée, the finest of these solutions, features a tapered cone next to the barrel and connects the two elements with a chain finer than any other in a jeweller’s possession. When the mainspring is wound and the tension is high, the chain pulls from the narrow top of the cone, where a short radius dampens its force; as it unwinds, the chain moves down towards the wide base, where a longer radius provides greater grip for the weakening pull. The force emerging from the cone – dampened at one end and amplified at the other – is delivered more consistently than was the case with the force emerging from the barrel. When, in 1994, A. Lange & Söhne miniaturised a mechanism of this type in a 38.5-millimetre wristwatch (“Pour le Mérite” Tourbillon), it astonished an audience that had taken it for granted that it was impossible to produce one at that size.
The Maltese cross also corrects the source, but in a distinct manner — by enclosing it rather than graduating it. Imagine a small cross-shaped wheel next to the mainspring barrel, with four rounded arms. Three have concave ends, slightly hollowed out to accommodate the pin; the fourth is convex, solid and protrudes slightly more. The pin, fixed to the barrel arbor, moves the cross by one tooth with every turn — just as a finger pushes the hand, click by click. As winding continues, it reaches the convex tooth: the opposite curvature, instead of offering a recess, stands in its way, and the pin comes to a halt against it. The barrel cannot be wound any further.
If the barrel is allowed to turn long enough in the opposite direction — as the spring unwinds — the same arm also prevents it from uncoiling completely. What is eliminated is not the irregularity itself, but its two worst moments — the initial violent turns and the final weak ones — leaving only the reliable central section in play. Both are attempts at reform: both assume that the defect lies at the source and can be rectified before the energy is set in motion; neither calls into question the premise that the energy released by the barrel, once corrected, must still complete the entire long journey to the balance wheel.
Isolation, not correction
The remontoir operates on the opposite principle: it does not correct the path of the energy, but refuses outright to allow it to reach the balance wheel. Near the end of the wheel train, as close to the balance wheel as the watchmaker dares, a second, tiny, independent spring is fitted. At regular intervals — once a second, once every eight seconds, once every four minutes, depending on the watchmaker — the energy from the mainspring is briefly channelled to this small spring to recharge it. The moment this happens, the connection is severed: the mainspring is bypassed and, for the remainder of the interval, it is the secondary spring, and that alone, which powers the balance wheel. The two never perform the same task simultaneously: the mainspring recharges the secondary spring with short, regular pulses; whilst the secondary spring rotates the balance wheel, moment by moment. The remontoir is, in effect, a battery situated at the far end of the movement, recharged in small increments and designed to deliver the same clean impulse every time. Whatever happens upstream — friction, wear, winding that is too tight or too slow — is kept at bay.
Four interpretations
Every remontoir operates within the same narrow scope: the final stage before the balance wheel. Observe four of them and you will see four interpretations answering a single question. The first to translate this idea into a production wristwatch did so in 1999. François-Paul Journe reasoned that a tourbillon, being heavier than a standard balance wheel, would be even more sensitive to fluctuations in energy from the mainspring barrel. In his Tourbillon Souverain, the remontoir halts the gear train once per second, disconnects the tourbillon from the mainspring and allows the small spring to drive the cage on its own; in a subsequent development (2003), Journe linked the seconds hand to it, so that it advances in one-second increments. Looking at the dial, the hand does not glide: it remains still for most of a second, then jumps to the next mark, more like a metronome than a blurred line — not so much to indicate the seconds as to give substance to the underlying mechanism that keeps them precise.
Andreas Strehler, who describes himself as an engineer for luxury brands and a watchmaker for a select few, arrived at his own version in 2013, drawing inspiration from a striking watch from the 1960s, in which a satellite wheel stabilised the oscillation of the striking mechanism. Adapting this solution to a wristwatch required miniaturisation, and Strehler knew just how far he could push the limits: a spring reduced to its smallest dimensions becomes fragile. So, rather than shrinking everything down, he positioned a compact assembly directly above the seconds wheel. At the centre is a star-shaped wheel: each of its points is held in place, one at a time, by a ruby mounted on a lever integral with the seconds wheel. As long as the ruby holds a point, the star remains locked — and it is the only component to receive the impulse from the barrel. But the seconds wheel turns ceaselessly and, carrying the ruby with it, gradually moves it away from the point until it releases it. The star then springs forward one step and, in doing so, winds up its own small spring — the one which, drawing energy from the mainspring barrel, drives the seconds — until the next point encounters the ruby again and comes to a halt. Locking, releasing, winding up: a mechanical breath, one for every second.
Arnold & Son adopts Strehler’s mechanism almost to the letter in the 2015 Constant Force Tourbillon, with just two differences: the ruby that holds the star in place becomes a locking pin, and the star wheel no longer drives the seconds alone, but is coupled to a tourbillon. A support is positioned straddling the seconds wheel and, at its centre, a star-shaped wheel is held in place by a locking pin: for most of each second, that pin simply locks onto a tooth of the star, just as the arm of a turnstile holds a single person at the entrance. Once every second, the pin advances just enough to release that tooth; the support snaps forward, propelled by the barrel, rewinds the remontoir spring, until the next tooth reaches the pin and is in turn locked in place. The seconds hand jumps on the left-hand side of the dial whilst a tourbillon rotates ceaselessly on the right — discrete, protected moments set against continuous motion.
Greubel Forsey employs the differential twice, each time for a different purpose. In the 2016 Double Balancier à Différentiel Constant, it pairs two balance wheels inclined at 30°, each beating independently; due to their inclination, they are always in complementary positions, and a differential averages their rates, dampening positional error — the very same error that the tourbillon corrects by rotating a single oscillator, and which is addressed here with two balance wheels instead of one. Constant force is provided by two tiny spiral springs mounted on the differential: rewound by the mainspring every four minutes, they supply the balance wheels with a constant impulse even as the barrels run down over the seventy-two-hour power reserve. The entire assembly rises above the movement in a tower visible from the dial side, and at the top of it a disc rotates to mark each infrequent rewind — so slow that observing it rewards patience rather than attention: an instrument built to read another instrument.
The second mechanism addresses a different problem. Even when reset every second, a remontoir does not deliver a perfectly uniform impulse to the balance wheel: a balance wheel operating at 21,600 vibrations per hour receives six impulses within that second and, as the spring unwinds progressively, those six impulses are not equal — the first is stronger than the last. In the 2018 Différentiel d’Égalité, Stephen Forsey employed a differential to smooth out that residual variation: not, as in the Double Balancier, to average the outputs of two balance wheels, but to equalise the force of a single one, delivering a continuous flow to the escapement rather than a succession of jerks. Whereas the first differential averages two oscillators and dampens the deviation between their positions, this one evens out a single force and mitigates the error in its intensity.
A question of lineage
Every mechanism to date, however ingenious, is constructed from the same two elements: a spring and the wheels that wind and release it. The purest solutions dispense with the wheels — and with them the very idea of a spring that needs rewinding: the constant impulse is no longer drawn from a reserve, but arises from the very action of the elastic element that produces it. The insight came from a Rolex watchmaker, Nicolas Déhon; what made it feasible was silicon, which can be shaped into forms impossible for steel — a thin strip that flexes and snaps between two positions with the same force at every beat. Girard-Perregaux has made this the heart of its Constant Escapement. In terms of constant force alone, silicon clearly outperforms spring-driven remontoirs; yet it inspires less devotion, for a reason that has nothing to do with performance but with lineage. A spring wound and released by wheels belongs to the most ancient art — brass, steel, the patience of the hand — whilst silicon achieves the same end by a means that tradition does not fully recognise as its own.
Which brings us back to the wrist and the small jumping hand from which we began: a watch, like most of those that still feature a remontoir, constructed according to the ancient discipline of springs and wheels. It seems the most ordinary thing on the dial. But now you know what lies behind it: a spring near the balance wheel, wound in small increments, which holds in reserve a single precise impulse against whatever the barrel might hurl at it — and behind that spring, generations of watchmakers who could not accept that the final moment of such a long and loss-ridden journey should be left to chance. The hand gives a little jump. Somewhere, out of sight, the little spring is released, caught, and released again. The second it marks is exact, and it is exact by design.
About the Author
Swiss-based independent writer specialising in the luxury watch industry, consultant to private collectors and investors, and contributor to Italian and international watch publications. A Watch Expert certified by the FHH, he is the editor of WatchDossier (watchdossier.ch), a publication dedicated to the cultural and philosophical trends in contemporary watchmaking. He is the author of Against the Grain: A Cultural History of Swiss Independent Watchmaking.
No compensation or brand affiliation influenced this essay. Opinions are the author’s own.
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